In idle CPU and GPU temperature drop to 54°C and 55°C respectively which seems fine to me (although I can't remember what they were in v8.2.5), but I would guess about the same.
I still can't boot v9 from stick, just tried the recent v9.0.2 which exhibits the same problem (black screen). Inplace upgrade from 8.2.5 worked here as well. I haven't yet checked screen settings or GPU temperature.
The 9.0.1 image won't even boot on my Xtreamer Ultra 2 which is currently running 8.2.5. After the bootloader the screen stays black forever (no splash screen). The same USB stick boots fine in a different box.